Countercurrent froth flow flotation system



June 1944- J. w. THOMPS ON ET AL 2,350,943

COUNTER CURRENT FROTH FLOW FLOTATION SYSTEM Filed March 2, 1940 4Sheets-Sheet l .1 /4. Flam/=50 5 4.5500711 .Rtorncu 1944- J.W.QI'HOMPSON ETAL 2,350,943

COUNTER CURRENT FROTH FLOW FLOTATION SYSTEM Filed March 2, 1940 4Sheets-Sheet a llll ll lllllll ll TTE NW 5 W5 JL 1 Gttorneg June 1944-J. w. THOMPSON ET AL COUNTER CURRENT FROTH FLOW FLOTATION SYSTEM FiledMarch 2, 1940 4 Sheets-Sheet 4 Ti rm? mm m mm Huh-kl Patented June 6,1944 COUNTERCURRENT FROTH FLOW FLOTATION SYSTEM John W. Thompson andLionel E. Booth, Salt Lake City, Utah, assignors to The GaligherCompany, Salt Lake City, Utah, a corporation of Utah Application March2, 1940, Serial No. 321,840

11 Claims.

This invention relates to a countercurrent froth flow flotation systemwhich is advantageously applied to concentration of metallurgical pulpsbymeans of flotation.

The principal objects of the invention are:

First. To produce a higher grade of concentrates by the so-calledrougher cells of a flotation machine.

Second. To decrease or eliminate the amount of middling return. I

Third. To improve the metallurgical efliciency of flotation generally.

' water.

Fourth. To increase themetallurgical capacity I of flotation machines.

Fifth. To decrease or eliminate the amount of spray or wash water usedin launders.

Sixth. To reduce floor space requirements.

Seventh. To allow the direct filtration of flotation concentrates.

Eighth. To simplify the cleaning and re-cleaning operations.

Ninth. In comparison with prior practice, to reduce the quantity offrothing reagent required.

The manner of attaining the objects just outlined, and some of'theresulting advantages are set forth briefly in the following paragraphs.

(a) The froth is caused to travel from the tailing end of a flotationmachine unit towards the feed end and is discharged in proximitythereto. In the course of its travel from the tail- 3 ing end to thefroth discharge end, the froth drops any gangue orvalueless materialback into the pulp zone of the machine.

(b) A smaller amount of froth is discharged fin circulating loads a ndvbecause the spray and launder wash water is virtually eliminated.

fe kshort launders only are required at the pointof frothnischarge, andas a result, steep slopes can be used,'which discharge directly into apump box or any other convenient point for retreatment. j "f f ('j)- Thefloor space required, is reduced because of increased cell capacity andbecause of the elimination of side'launders for carryingoff the froth. Ir i (g) Laimders'are advantageously placed on steeper grades, therebyallowing for the direct discharge of concentrates to filters. I

(h) Rougher' froths' and-intermediate froths are advantageouslydischarged directly to cleaner or re-treatment cells without the use ofdilution This provides for extremely compact installations.

(2') Because less froth is removed from the flotation cells, lessfrothing reagents are required. I According to the invention, a liquidor semiliquid such as flotation pulp, is confined as a normally staticbody. Different parts of the pulp body are subjected to progressivelyvarying bubble generation, for example, by means of aeration oragitation in varying degrees, with the result that correspondinglyvarying masses of froth containing the valuable mineral of an ore underflotation treatment, are constantly building up on the surface of thepulp. The differences in the levels to which the froth builds up, createpotential fluid heads which cause the froth to flow by gravity from thehigher levels to the lower levels, and particularly to the lowest levelat one end of the pulp body where the froth which carries the finishedor partially finished concentrates, is advantageously discharged andsaved. The less valuable materials or tailings,

on the other hand, are caused to flow counter to the flow of the froth,and are discharged at the other end of the pulp body. This isaccomplished by causing the maximum degree of progressive. aeration oragitation to take place in proximity to the point of discharge of thetailings.

An advantage of this novel arrangement is that worthless particles organgue, which may inadvertently be carried up through the pulp by the 3rising froth, are promptly dropped back into" the current of ta'ilingsand discarded as waste. The novel characteristics of the machine of theinvention make feasible many original combinations of individualflotation multiple cell units, as will'hereinafter be more fullyexplained. By means of such combinations, large savings in originalplant cost, in operating time and expense, and in the cost of reagentsmay be ef fected.

' Apparatus for practicing the invention may advantageously comprise aplurality of individual flotation cells arranged together in series toform a-niultiple cell unit in which free communication "among theconstituent cells, as well as a common pulp level, are maintained, whileat the sametime, 'the'cell's are operatively distinct one from Each cellis advantageously provided with its individual froth generator, and eachfroth generator is regulable according to the'quantity of froth requiredat its own particular location in the sequence of operations of themultiple cell unit as a whole. The pulp feed isintroduced into the firstcell, advantageously at a point low in the pulp body, and is conductedsuccessively through the remaining cells of the unit, until used at thetaillngs end of a flotation machine,

while progressively smaller quantities of air are used in the successivecells of a series until the first cell at the head end is reached.

The froth containing the valuable minerals of an ore under treatment,progresses from the last cell towards the head end where it isdischarged from cell No. 1 in the form of finished or partially finishedconcentrates, the latter being conducted to a cleaning flotation machinewhich may or may not utilize the countercurrent I froth flow feature.

In the accompanying drawings, which illustrate specific embodiments bymeans of which the invention is advantageously put into practice,

Fig. 1 represents in plan, a flotation machine comprising for example,four cells;

Fig. 2, a longitudinal, verticalsection taken on the line 2'-2 in Fig.1, pipes in the background being omitted;

Fig. 3, a cross-section taken on the line 3-3 in Fig. 2;

Fig. 4, a diagrammatic plan, corresponding to Fig. 1 and serving as anucleus around which the succeeding Figures 5 to 28 are developed;

Fig. 5, an arrangement similar to Fig. 4, but arranged for producing abetter grade of concentrates withoutmiddling returns;

Figs. 6 and '7, respectively, a diagrammatic plan and correspondingfront elevation showing an arrangement for re-treatment or cleaning ofconcentrates from multiple cell rougher units;

Figs. 8 and 9, respectively, a diagrammatic plan and corresponding frontelevation operatively similar to Figs. 6 and 7, but having the cleanercells turned through an angle of 90 degrees for straight flow ofconcentrates over the end of machine for the purpose of economizlngshowing the manner in which cells may be added for greater capacity;

Figs. 12 and 13, respectively, diagrammatic plan and corresponding frontelevation of an arrangement of cells for double cleaning treatment ofmetallurgical pulp;

Figs. 14 and 15, respectively, a diagrammatic plan and front elevationshowing rougher cells with a drop in elevation between each group offour cells, which facilitates the control and feeding of reagents incertain cases; g

Figs. 16 and 17, respectively, a diagrammatic plan and front elevationof a cell arrangement similar to that shown in Figs. 14 and 15,,buthaving the cleaner cells turned through an angle of 90 degrees, for thepurpose of giving the concentrates a right line flow through the machineand at the same time accomplishing an economy in floor space;

Figs. 18 and 19, respectively, a diagrammatic plan and front elevationof a cell arrangement having the advantages of operation of those shownin Figs. 16 and 17, but providing for a more compact floor disposition;

Figs. 20 and 21, respectively, a diagrammatic plan and front elevationof a cell arrangement having-operative characteristics similar to thoseof the arrangement in Figs. 14 and 15, but showing an especiallyadvantageous floor arrangement;

- Figs. 22 and 23, respectively, a diagrammatic plan and front elevationof an arrangement having the advantages of that shown in Figs. 14 and15, but in which the cleaner cells are parallel to the rougher cells,and more cleaner cells are provided for;

Figs. 24 and 25, respectively, a diagrammatic plan and front elevationof an arrangement of rougher-cells having a drop in elevation betweenthem as in Figs. 14 and 15, but providing for double cleaning;

Figs. 26 and 27, respectively, a diagrammatic plan and front elevation,of a cell arrangement which accomplishes operative results similar tothose accomplished in the arrangement of Figs. 24 and 25, but providingfor a considerably more compact floor disposition; and

Fig. 28, an end elevation in diagram, viewed Referring to the drawings,Figs. 1, 2 and 3 show a flotation machine which includes much of themechanism forming the subject of United States Patents Nos. 2,055,065and 2,085,947, granted to Lionel E. Booth. This mechanism'has novelfeatures which are particularly well adapted for use in combination withthe present invention.

Patent No. 2,055,065 is concerned with a rotatable impeller comprising atight walled, substantially bell-like structure along the lowercircumference of which a plurality of depending teeth or lugs are spacedapart from one another. Compressed fluid, such as air, is conducted intothe hollow interior of the bell, and this air is caused to bubblethrough the spaces between the depending teeth, into the surroundingpulp. The size of the bubbles is determined largely by the speed ofrotation of the impeller, while the quantity of bubbles generated isadvantageously regulated by the amount of compressed air admitted intothe bell.

Patent No. 2,085,947 is concerned with peeling blades that areadvantageously disposed radially around the impeller just described, inorder to conduct the copious flow of bubbles from the impeller upwardlythrough the pulp, thereby preventing a congestion of bubbles around theimpeller, and thus enhancing the efllciency thereof.

In Figs. 1,2 and 3, the numeral 40 denotes a structure embracing foursuccessive individual cells I, 42, 43 and 44, the one at M beingregarded as the head cell and the one at M, the tail cell. The pulp isadvantageously introduced into head cell 4| through an inlet opening 46located at the-bottom of a feed box 45, the inlet opening beingadvantageously located low in the cell structure.- In this cell, thepulp is exposed to the proper means for producing a certain desiredamount of froth which rises through the pulp body 41 and into the space"-4 above the pulp surface 49. The pulp body is caused to travelsuccessively through the cells ll, 42, 43 and 44 in the generaldirection of the arrow 53. During the movement of the pulp through therespective cells, it is exposed to a graduated increase in frothgeneration, which results in a correspondingly greater quantity ofbubbles rising through the pulp from cell to cell until thelast cell isreached, where the froth production in the present example, is at themaximum. This 2,360,943 results in building a body of froth 48 which isdeeper at 48-2 than it is at l8-I', whereby a fluid or hydrostatic headis created approximately along the gradient 59. The froth beingextremely mobile, tends to find its fluid surface level because ofgravity, and in so doing, a quantity of froth is continually beingpushed in the direction of the arrow 54, from the higher froth levels tothelowest froth level, at which latter point it overflows the frothdischarge weir to be disposed of as desired.

A hollow, tight-walled impeller is indicated at 56, it being rigidlymounted on a rotatable shaft 61, supported and driven in any suitablemanner (not indicated). Spaced apart from one another along the lowercircumference of the tightoccupied, combined with maximum performanceand output of the flotation machine. For the purpose of giving at leasta partial understanding of walled portion 56 of the impeller aredepending lugs 55, and projecting upwardly into the interior of theimpeller is a pipe 58 through which compressed air is discharged. Thecompressed air reaches the pipe 58 through the pipe assembly 59 from amain supply header 69, and the flow of compressed air from the header tothe impeller may be controlled by a valve 6 I.

In operation, assuming the impeller to be rotating at the proper speed,which may vary from 1209 to 1900 f. p. m. and assuming the proper amountof compressed air to be flowing into the impeller, the compressed airbubbles through the spaces 62 between the lugs 01' the impeller. Theincipient bubbles are clipped into extremely small bubbles which inrising through the pulp, pick up the mineral and form the froth masses.F. p. m. indicates peripheral feet per minute.

The fine bubbles which are discharged by the impeller are guidedupwardly through the froth by means of the peeler blades 63, 64 and 65.it being understood that the number and arrangement of the peeler bladesare not restricted by ,the showing in the present drawing, whichrepresents merely a suggestive arrangement.

The impeller 56 and rotatable shaft 51 are duplicated at 56-I to 56-9,and ST-I to 513, respectively, in the respective cells 92 to M. Thepeeler blades 63 to 65 are also duplicated in the cells 42 to 44,although the duplicates are not shown in the figures.

The amount of froth generated in the successive cells may advantageouslybe controlled or regulated by precisely varying the relativeamounts ofcompressed air admitted into each respective impeller, by means ofvalves 6| to '6I3. It is also possible to vary th generation of froth inthe successive cells by varying the speeds of rotation of the respectiveimpellers 56 to 56-3.

In order to provide .for the freeflow of the froth, as well as for thefree counterflow of the tailings, it is advantageous to separate thedifferent cells one, from another, by comparatively low baflles, such asthose indicated at 67 in Figs. 1 and 2. The sidewalls '68 and 69 andendwall I9 serve to confine the froth to. the channel formed over thesurface of the, pulp. and to compel the froth to be discharged at theweir 5!, as hereinbefore mentioned. The tailings stream mayadvantageously be discharged over ayweir II, and disposed of as desired.Both the weirs 5| and Il may consist of removableflashboards for varyingthe relative heights thereof.

; .'I'he multiple cell system of constructiqn is very elastic and adaptsitself to an almost endless the many combinations of cells that can beadvantageously made to meet difierent requirements, a few of thepossible'combinations are further illustrated in diagrammatic form inFigs. 5 to 28.

The arrangement in Figs. 6 and 7 is one for positive re-treatment orre-cleaning of rougher concentrates. In this arrangement the feed entersat I6 and passes through the four rougher cells 18, discharging thetailings at 19 and the rougher concentrates at 99, from where they passdirectly into the cleaner cells BI. The finished concentrates aredischarged at 82, while the cleaner tailings are discharged at 83 into apump 99, from where they are returned into the main feed '95. Forconvenience, the pump 94 is omitted in Fig. '7.

In Figs. 8 and 9 the arrangement is similar to that in Figs. 6 and 7,but the cleaner cells aI-I have their longitudinal dimensions at rightangles to the longitudinal dimension of the rougher cells I6. The pumpis indicated at 84-I, and the cleaner concentrates are discharged at82-I, cleaner tailings at 93I.

In Figs. 10 and 11. the cleaner unit 8I-I is similar to that in Figs. 8and 9, but the number of individual cells in the rougher unit 86, isincreased for greater tonnage. Here, the feed enters at 81. Therougherconcentrates are discharged into the cleaner unit at '86, and therougher tailings are discharged at 89. The cleaner tailings aredischarged at 99 and pass into the pump 9I from where they are returnedto the feed 81.

In Figs. 12 and 13, a double cleaning treatment is provided for. Thefeedenters at 92, and passes through the rougher unit 93, from which theconcentrates pass at 94 into theflrst cleaner unit 95.

The concentrates from the first cleaner unit pass at 96 into the secondcleaner unit 91. The tail ings from the two cleaner units are dischargedat 99 and 99 respectively, and in combination enter the pump I99 whichreturns them into the,

feed 92. The finished concentrates from the second cleaner unit aredischarged at It", while the total tailings are discarded from therougher unit.

a drop in elevation between the cells is provided for. This facilitatesthe control and feeding of reagents in certain cases. The feed entersthe first, rougher unit I93 at I96, and the concentrates from this unitare discharged at I91 into the cleaner unit m5. While the-tailingsaredis;

charged at; I98, passing into the second rougher unit I94, from wheretheconcentrates are,dis-.

charged at III and the tailings at-IIZ. I'he'tailings. from the cleanerunit I are discharged at.'

H3 and are passed to the pump I, being joined meanwhile by theconcentrates discharged at I II,

The arrangement of cells described in conneccarded at I41.

to be returned to the feed at m. The finished concentrates aredischarged at I I5.

gles to the longitudinal dimension of the rougher units HIS-l and ll4-I.

In Figs. 18 and 19, the arrangement is operatively similar to that inFigs. 16 and 17, but is more compact because the second rougher unitIl4-2 is placed in parallel with the first rougher unit I03-2 instead ofbeing in tandem therewith as in Figs. 16 and 17.

In Figs. 20 and21, the arrangement is operatively similar to that inFigs. 14 and 15 but provides for a different disposition as to floorspace. Here. the feed enters the first rougher unit III-lat HIS-3, whilethe tailings from the IIi4-l are discharged at second rougher unit 2-4.The finished concentrates are discharged at -3 from the cleaner unit"5-3.

- In Figs. 22 and 23 the general arrangement again is similar to that inFigs. 14 and 15, but more cells are included in the cleaner unittogether with a somewhat different floor arrangement. Here, the feedenters at IIB into the first rougher unit N1, the concentrates fromwhich pass at II8 into the cleaner unit IIS, while the ta lings pass atI2II into the second rougher unit The concentrates from the secondrougher unit are discharged at I22, and are ioinedby the tailings fromthe cleaner unit which are discharged at I23, the two going to the pumpI24 by which they are returned to the feed H6. The total finishedconcentrates are discharged at I25,

' and the total tailings are discarded at I26.

In Figs. 24 and 25, the arrangement provides for a drop in elevationbetween the two rougher units I21 and I28 for the same purpose as thatin Figs. 14 and 15, but includes the double cleaning feature by means oftwo cleaner .units I29 and III. The feed enters at III; the concentratesfrom the first rougher unit I21 pass at It: into the first cleaner unitI29, while the tailings from the first rougher pass at I83 into thesecond roug'her unit I28. The concentrates discharged at I34 from thesecond rougher, are merged with the tailings discharged at Ill-4 andI29-l respectively from the two cleaner units, and at I54 are pumpedback into the feed iii. The total concentrates are discharged at I35from the first cleaner unit, and the total tailings are discharged atI36 from the second rougher unit.

. In Figs. 26 to.28, the arrangement provides for the same generaloperative result as attained by that in Figs. 24 and 25, but at the sametime provides for conservation of fioor space. Here. the first rougherunit is indicated at I21, the second at I32, the first cleaner unit atI30, and the second cleaner unit at I40. The feed enters the firstrougher at I4I, while the concentrates from this rougher enter the firstcleaner unit I at I42. The tailings from the first rougher enter thesecond rougher at I43, while the concentrates from the second rougherleave at I, merge with the tailings from both the cleaner units and arereturned by means of the pump I45 to the feed I. The total finishedconcentrates are discharged at I46, while the total tailings are dis-The concentrates from the first cleaner I go through the passage I44into the second cleaner I40 and the tailings from the sec-v ond cleanerare discharged at I49.

The structure illustrated in Figs. 1 to 4, may

' of the structure.

be described as composed of the individual cells 4i to 44, or it mayconsistently be regarded as embracing only a single cell whoseconfiguration is longitudinally extensive and which is provided withmeans for quantitatively graduated froth generation from end to end, orin which froth generators are spaced apart from one another along thelongitudinal dimension with means for precisely varying the productionof froth by the successive generators. If desired, the battles 51 maysometimes be omitted, which still further emphasizes the single cellviewpoint.

In any event, the distinguishing feature of the machine is always theopen and substantially unobstructed passage for pulp and froth incountercurrent relation to each other from end to end various assembliesof units shown in Figs. 5 to 24, as well as to the unit shown in Figs. 1to 4. For example, the assembly as shown in Figs. 12 and 13,,c0nsists ofthe three units 83, 85 and 21, where the passage through the rougherunit 93 is open and unobstructed from the end I5| to the other end I52,although including six individual impeller spaces each provided with itsown impe1ierI53.

Again, in the same figures, the open passage through the first cleanerunit 95 extends from the end I54 to the other end I55, and in the secondcleaner unit 91, from the end I55 to the other end I51.

Another example is the assembly in Figs. 26 to 28. Here the open passagethrough the first rougher I31 extends between the ends I58 and I59; theopen passage through the second rougher I38, between the ends I60 andI5I; the open the ends I62 and I83; and through the second cleaner I40,between the ends I64 and I65.

In the most advantageous form of the machine, the two sidewalls, such as68 and 69 in Figs. 1 and 2, are sufllciently high so that the froth isprevented from overflowing excepting at the end weir 5|. There are timeshowever, when it becomes desirable to discharge the froth over eitherone or both sidewalls. In such cases these walls are provided withremovable flashboards, for example, such as those shown at I1II, I1I,I12 and I18. When these flashboards are removed, the froth may overflowat suitably graduated levels, for example, those represented by thebottom edges of the fiashboards, which in this instance follow closelythe gradient 50. By removing such flashboards in various combinationsthereof, almost any desired control may be exercised over the sidewallfroth discharge. The sidewall discharge of froth may be carried off byany suitable means, for example, by launders "4..

The invention is characterized by the countercurrent relationshipexisting between the froth flow and the flow of theat-least-partially-impoverished pulp or tailings, as herelnbeforeexplained. It should be remembered however, that while the froth flow inthis relationship is along the substantially level surface of the pulpbody, the counterflow of the pulp and its suspended tailings is notlikewise substantially horizontal.-

In fact, it is only the net transportative displacement of the pulp andits tailings that is horizontal, because both are subjected to thevarying upwardly directed impulses in the successive bubble columnzones. This variation causes many of the pulp particles, includingtailings, to circulate upwardly and downwardly during the progress ofthis horizontal displacement.

This viewpoint applies to the at the weir ll accordingly.

The aerating mechanism of the aforementioned Patent 2,085,947 isespecially well suited for use in combination with the presentinvention, because air or other fiuid is admitted to the impeller underpressure, usually from threefourths to one and one-half pounds persquare inch. The flow of this compressed fluid through each successiveimpeller, is subject to accurate control, whereby the requirements ofthe invention for precisely differentiated generation of fluid bubblesto form froth in differential quantitles at the corresponding localitieson the surface of a pulp body, are fully accomplished.

It is the ability to control the constant formation of froth at definitepoints and in certain predetermined quantities that makes possible thegravity flow of the froth across the surface of a pulp body inopposition to the movement of the pulp body, which in this instance isin the direction of the weir H, and occasioned by the overflow at thatpoint. a

In ordinary flotation, froth is removed along the full length of amachine. .Since large proportions of the reagents used, are removed withthe froth, the frothing properties towards the tail end of a machine arematerially diminished, frequently to a point where it is diilicult tomaintain a froth overflow at all at this end of the machine.

In using the countercurrent flow feature, it is to be noted that sincethe froth breaks down in traveling from the tail end to the head end,water composing the bubbles, together with reagents, is dropped backinto the pulp body and is again carried towards the tail end .of themachine, thus using this part of reagents over and over again.

Performance of the countercurrent froth flow system compared withperformance of what has heretofore been regarded as standard practice,in actual operating tests, gave results as follows:

Test N0. 1

Zn Fe Insol.

C. C. F. F. system: Percent Percent Percent Concentrates 63. 0. 2. l'lailing 1.3 Stfiidlard practice at Silver King 1 (on centrates 63. 2 0.8 l. 3 'Iailing 1.6

Test N0. 2

Zn Fe Insol.

C. C. F. F. system: Percent Percent Percent Concentrates a 62.6 0.Tailing 1.1 stgllllflllllld practice at Silver King i i Concentrates63.0 0. 8 l. 6 Ta 'ng. 1.0

It will be noticed that the concentrate recova cries and tailing lossesare practically the same for both the countercurrent froth flow testsand invention, are self evident. The direct savings in reagentshereinbefore dwelt upon, are in addition to the savings just enumerated.

Having fully described our invention what we claim is:

1. A method of counter-current froth-flow flotation, comprising feedingflotation pulp substantially constantly into one end of a normallystatic, longitudinally extended body of flotation pulp which hassubstantially uniform width, thereby imparting a substantially constant,and substantially unidirectional, longitudinal displacement ortransition to the pulp body and causing pulp to discharge at theopposite end of the pulp body; introducing air into' the transient pulpbody in graduated quantities from end to end thereof, the greatestquantity being introduced at the said pulp discharge end; andaccumulating the resulting bubbles in the form of froth on the surfaceof the pulp body substantially in the proportion of air introduction atcorresponding points along the length of the pulp body, thereby forminga hydrostatic head of froth, and causing the said froth to flow bygravity along the surface of the pulp body counter to the direction oftransition of the pulp, by confining the said froth against discharge atsaid pulp discharge and and laterally along the length of the pulp body.

2. A method of counter-current froth-flow flotation, comprising feedingflotation pulp into one end of a normally static, longitudinallyextended body of flotation pulp which has substantially uniform width,thereby imparting a substantially constant, substantiallyunidirectional, longitudinal displacement or transition to the pulp bodyand causing pulp to discharge at the opposite end of the pulp body;conducting the transient pulp one into another, the said frothgenerating zones extending from near the locality of feeding pulp tonear the locality of discharging pulp; generating froth in thesuccessive generating zones with increasing intensity of generation fromzone to zone, the least intensity being in promixity to the locality offeeding pulp, and the greatest in proximity to the locality ofdischarging pulp, thereby causing froth to rise, to the surface of thepulp body in quantities which are substantialy proportional to thesuccessive intensities of generation; and. accumulating the said frothon the surface of the pulp body as it rises, thereby forming ahydrostatic head of froth, and causing said froth to flow by'gra'vityalong the surface of the pulp body counter to the'direction' oftransition of the pulp, by confining the said froth against discharge atthe locality'of discharging pulp and laterally along the length of thepulp body substantially up to the vicinity of said local ity of feedingpulp. I I

3. A method of counter-current froth-flow flotation, comprisingmaintaining a longitudinally extended body of flotation pulp havingsubstantially uniform width; introducing air into the lower portion ofthe pulp body in successively graduated quantities from maximum tominimum along the length thereof and within an aerating zone which issubstantially coextensive horizontally with the said pulp body, to formbubbles which rise through the pulp body and to the surface thereof insubstantially correspondingly graduated quantities; continuouslysupplying additional pulp to the pulp body near one end thereof andcontinuously discharging tailings near the opposite end thereof, therebycausing the aerated pulp to fiow in a substantially continuous,substantially unidirectional longitudinal stream from the pulp inflowend of the pulp body to the tailings discharge end thereof andimmediately above said aerating zone; accu-' mulating the bubbles. inthe form of froth at the. surface of the pulp body substantially in theproportion of air introduction at corresponding points along the lengthof the pulp body, thereby forming a hydrostatic head of froth, andcausing the said froth to flow by gravity along the surface of the pulpbody counter to the direction of transition of the pulp, by confiningthe said froth against discharge at said tailings discharge end andlaterally along the length of the pulp body; and discharging said frothfrom the surface of the pulp body near said pulp inflow end thereof.

4. A method, as recited in claim 3, wherein a minor part of the froth isdischarged at a locality or localities situated between the two endextremities of the pulp body.

5. A flotation machine, comprising an elongated container adapted tohold a body of pulp; aeration means disposed in an aerating zone definedat a low level within said container and said means extending along thelength thereof; pulp inflow means disposed near one end of saidcontainer; tailings outflow means disposed near the opposite end of saidcontainer; froth outflow means disposed at the upper part. of saidcontainer near said pulp inflow means; and means for effecting flow offroth along the surface of said body of pulp substantially from thetailings-outflow end of said container to the said froth dischargemeans, said container having its interior, above said aerating zone,substantially free and unobstructed so pulp may flow substantiallyhorizontally, substantially unidirectionally, and longitudinally, fromsaid pulp inflow means to said tailings outflow means and within a zonedisposed above said aerating zone.

6. A flotation machine, comprising an elongated container havingsubstantially uniform width and adapted to hold a body of pulp; aerationmeans disposed in an aerating zone defined at a low level within saidcontainer and said means extending along the length thereof; pulp inflowmeans disposed near one end of said container; tailings outflow meansdisposed near the opposite end of said container; froth outflow meansdisposed at the upper part of said container near said pulp inflowmeans; and means for regulating the supply of ,air to said aerationmeans so that said supply of air will be a maximum near thetailings-outflow end of said container and a minimum near thepulp-inflow end of said container, resulting in the building up of ahydrostatic head of froth upon the surface of the body of pulp at thetailings-outflow end.

of said container, and in the gravity flow of froth from saidtailings-outflow end to said pulp-inflow end of the container duringoperation of said flotation machine, said container having its interior,above said aerating zone, substantially free and unobstructed so pulpmay flow substantially horizontally, substantially unidirectionally, andlongitudinally, from said pulp-inflow means to said tailings-outflowmeans and within a zone disposed above said aerating zone.

7. A flotation machine, comprising an elongated container adapted tohold a body of pulp,

said container having its lower portion partitioned off at intervalsalong its length transversely of its width forming individual aerationcells; mechanical aerating means disposed in the respective aerationcells; pulp inflow means disposed near one end of said container;tailings outflow means disposed near the opposite end of said container;froth outflow means disposed at the upper part of said container nearsaid pulp inflow means; and means for effecting flow of froth along thesurface of said body of pulp substantially from the tailings outflow endof said container to the said froth discharge means, said containerhaving its interior, above said aeration cells, substantially free andunobstructed so pulp may flow substantially horizontally, substantiallyunidirectionally, and longitudinally, from said pulp inflow means tosaid tailings outflow means and within a zone disposed above saidaeration cells.

8. A flotation machine, comprising an elongated container havingsubstantially uniform width and adapted to hold a body of pulp; saidcontainer having its lower portion partitioned off at intervals alongits length transversely of its width forming individual aeration cells;mechanical aerating means disposed in the respective aeration cells;pulp inflow means disposed near one end of said container; tailingsoutflow means disposed near the opposite end of said container; andmeans for regulating the extent of aeration within the respectiveaeration cells so that the aeration will be a maximum near the tailingsoutflow end of said container and a, minimum near the pulp-inflow end ofsaid container, resulting in the building up of a hydrostatic head 'offroth upon the surface of the body of pulp at the tailings outflow endof said container and in the gravity flow of froth from said tailingsoutflow end to said pulp inflow end of the container during operation ofsaid flotation machine,

said container having its interior, above said aeration cells,substantially free and unobstructed so pulp may flow substantiallyhorizontally, substantially unidirectionally, and longitudinally, fromsaid pulp inflow means to said tailings outflow means and within a zonedisposed above said aeration cells.

9. In a flotation system, a plurality of flotation units interconnectedin series arrangement to effect a single final discharge of froth, eachof said flotation units comprising an elongated container for pulp.having substantially uniform width and defining along its length a loweraeration zone, an intermediate separation zone; and an upper frothtransportation zone, the said separation zone and froth transportationzone extending substantially free and unobstructed along substantiallythe entire length. of the said container, the container having pulpinflow means and froth outflow means near one of its ends, and tailingsoutflow means near its opposite end, and having further, means foraerating pulp differentially substantially from end, to end of saidaeration zone, the locality of greatest aeration being near the tailingsoutflow end of the the pulp body and within said froth transportationzone during operation of said system, whereby froth flows along saidfroth transportation 10 zone toward said froth outflow means under theinfluence of gravity, and pulp flows substantially unidirectionallycounter thereto; and respective passage means connecting the said frothoutflow means of each of the said flotation units, except the last, withthe said pulp inflow means of the next succeeding.

10. A method of countercurrent flotation comprising, maintaining alongitudinally extended body of flotation pulp; introducing air into thelower portion of the pulp body, within an aerating zone which issubstantially coextensive horizontally with the said pulp body, to formfroth which rises through the pulp body and accumulates at the surfacethereof; continuously supplying additional pulp to the pulp body nearone end thereof, and continuously discharging tailings from the pulpbody near the opposite end thereof, thereby causing the aerated pulp toflow in a substantially continuous, substantially unidirectional,longitudinal stream from the pulp inflow end of the pulp body to thetailings discharge end thereof and immediately above said aerating zone;flowing the said accumulated froth on the surface of the pulp body andalong the length thereof from near said tailings discharge end of thepulp body toward the said pulp inflow end thereof; and discharging saidtruth from the surface of the pulp body near said pulp inflow endthereof.

11. In a flotation system, a plurality of flotation units interconnectedin series arrangement to eflect a single flnai discharge of froth, eachof said flotation units comprising an elongated container for pulpdefining along its length a lower aeration zone, an intermediateseparation zone,

15 and an upper froth transportation zone, the said units, except thelast, with the said pulp inflow 9 means of the next succeeding.

JOHN W. THOIWPSON. LIONEL E. BOOTH.

